1. Field of the Invention
This invention relates to a wear-resistant member of cermet, such as a blade member for a cutting tool, having a hard coating which exhibits excellent wear-resistance and toughness.
2. Prior Art
There have been extensively used surface-coated wear-resistant tool members, such as a blade member for a cutting tool, which comprise a substrate of cermet ,such as cemented carbide including tungsten carbide (WC) and titanium carbidebased cermet, and a hard coating formed on a surface of the substrate and comprising one or more layers each composed of one of titanium carbide (TiC), titanium nitride (TiN), carbonitride of titanium (TiCN), oxy-carbide of titanium (TiCO), oxy-nitride of titanium (TiNO) and oxy-carbo-nitride of titanium (TiCNO). In some cases, such a coating further comprises an outermost layer of aluminum oxide (Al.sub.2 O.sub.3) which is either in the amorphous form or the crystalline form.
Although such a conventional hard coating exhibits excellent wear-resistance, it is inferior in toughness, so that a crack can easily develop in the coating when the coating is subjected to bending stress during the operation of the wear-resistance tool member. In addition, this crack can be transmitted to the substrate of the tool member, so that the resistance of the tool member to breakage or damage is considerably lowered.
In order to overcome this difficulty, it has been proposed to form a coating of the above-mentioned titanium compounds by physical vapor deposition in such a manner that the thickness of the coating is kept as thin as possible and that the vapor deposition is carried out at temperatures of not more than 600.degree. C. to make the structure of the coating fine and less crystalline. This coating on the wear-resistant tool member can be suitably deformed when subjected to bending stress to prevent a crack from developing in the coating, thereby ensuring that the resistance of the tool member to breakage is not lowered. This procedure has been found not entirely satisfactory, however, in that such a coating can not achieve a required wear resistance because the coating is thin and less crystalline.